The invention relates to a correlator comprising a chain of at least two cascaded delay members, the first of which receives an input signal comprising pulses in periodical intervals and being present as a series of digital sampling values, and a combination circuit for linearly combining the input signal of the first delay member and the output signals of all delay members and for generating by the occurrence of a pulse a correlator output signal assuming an extreme value.
A correlator of this type may be used, for example, in a television receiver for detecting the synchronisation pulses in a noisy television signal.
The correlation function between an input signal and an available specimen signal is formed by means of a correlator. The correlation function gives an indication about the similarity of two signals. For example, a periodical pulse-shaped signal whose variation is qualitatively known, but which is beset with noise and is therefore unrecognisable can be detected by means of a correlator. The output signal of the correlator, the correlation function, assumes an extreme value in the case of a pulse so that the instant of occurrence of the pulses can be determined.
A correlator consisting of a chain of cascaded delay members the first of which receives the pulse-shaped input signal and which members each store one sampling value is known for example from the book by Eugen Philippow, "Taschenbuch Elektrotechnik", Vol. 2, 1st edition 1977, page 171. The input signal and the output signals of the delay members are applied to a combination circuit (adder stage) via phase-shifting circuits possibly inverting the separate signals. The multiplication of the pulse-shaped specimen signal by the input signal which is required for forming the correlation function is realised by the phase-shifting circuits. In the combination circuit the correlation function multiplied by a constant is formed by linear combination (addition).